Neuropathic pain sensations are differentially sensitive to dextrorphan.

Rats with an experimental painful peripheral neuropathy (the CCI model) display heat-hyperalgesia and mechanoallodynia. Previous work has shown that the heat-hyperalgesia is suppressed by dextrorphan (DEX) and other N-methyl-D-aspartate (NMDA) receptor antagonists. The present work shows that when tested in the same rats, a dose of DEX that is maximally effective against heat-hyperalgesia has no effect on mechano-allodynia. The results suggest that different kinds of abnormal pain sensations may be caused by different pathophysiologic mechanisms that may respond differently to drug therapy.